It took over 20 years and a year pandemic for paleontologist To integrate the fossilized remains of the earliest ancestors of mammals and discover that their evolution that gave rise to modern humans may have begun in the Southern Hemisphere.
According to the team of researchers who created it, analysis of a small collection of tiny fossilized jawbones with characteristic molar teeth turns our understanding of when and where modern mammals evolved into heads.
Museums Victoria paleontologist Thomas Rich is a co-author of the new study and a longtime fossil hunter.
He was found on an Australian beach in 1997 after a 23-year search. mammalian jawbone It had strange teeth that were only seen in Europe and North AmericaThe jawbones are from small shrew-like creatures and date back to the Cretaceous period. dinosaur also walked around.
As the years went by, more and more mammalian jawbones Mesozoic Ages have been discovered: Madagascar, Argentina, India, and more recently also in Australia.
Measuring less than an inch in size, each of these specimens had unique molars. According to the latest analyzes that have reviewed them, the oldest fossils are about 50 million years older than those found in the northern hemisphere.
“These amazing series of discoveries have completely changed our long-standing theories about mammalian evolution. In fact, it turns our thinking about mammalian evolution upside down,” said Rich. . To tell.
The teen teeth in question are called tribosphenic molars, and the top and bottom mesh together to chop, crush, bore, and grind plant food and insect prey.
During the pandemic, respected paleontologist Tim Flannery and Australian Museum chief scientist Chris Helgen had the idea of revisiting the fossils of three tribosphenic mammals in Australia. Rich explained in 2020 – and began sifting through the scientific literature to see what else they could find.
They link these strange teeth to early mammal fossils found in the southern hemisphere, and that the Argentinian specimen is the oldest of the lot, millions of years older than the early mammal fossils found in the northern hemisphere. Recognized.
From there, they plotted another origin story for mammals. Mammal ancestors may have flitted between continents in the south when they came together in a supercontinent called Gondwana about 125 million years ago before heading north.
Based on the age and anatomical similarities of the fossils, the researchers believe they represent the earliest ancestors of marsupials (such as Australian koalas and wombats) and placenta (including humans). increase. bestial mammal.
“Our study shows that terriers evolved in Gondwana, thrived and diversified there over 50 million years before migrating to Asia in the early Cretaceous.” I will explain Hegren. “Once they arrived in Asia, they diversified rapidly, filling many ecological niches.”
Researchers suggest that the specialized molars of our earliest mammalian ancestors may have been key to their evolutionary success. But the evolution of early mammals that outlived dinosaurs A scientist who has long been fascinated Undoubtedly, it will continue to attract continued scrutiny.
In paleontology, as in any other science, the weight of evidence speaks volumes. And for more than 200 years, the diversity of mammals inhabiting the northern hemisphere and the abundance of fossils found there have led scientists to believe that the ancestors of placenta and marsupials originated in the north and spread south. .
However, studies show that the fossil record distorted by who is looking whereSo far, the only thing that has to challenge this long-held theory of mammalian origin is this small collection of tiny teeth, and it took decades to find even those seven specimens.
“This is the most important part of the world-wide paleontological study I have ever published, but it may take some time before it is fully accepted by researchers in the northern hemisphere. I can’t.” To tell Flannery.
It also took a long time to accept the results of the analysis. “I resisted conclusions as best I could, but the evidence is compelling,” Flannery said. Said Karen McGhee, science and environment editor at Australian Geographic, said:
In fact, not all paleontologists are convinced. While Flannery and team hold up this new revelation as a major discovery that upends our understanding of mammalian evolution, Flinders University paleontologist Gavin Prideaux said: To tell Their conclusions are based on the “smallest, crappiest little pieces” of fossilized teeth.
Another interpretation, as he told The Sydney Morning Herald, is convergent evolution: These tribosphenic molars evolved in several separate places around the same time. “The jury is out yet,” he said. To tell.
This research Alcheringa: Australian Journal of Paleontology.
